Adhesive materials have been used for the restorative care of wet bodies such as biological hard tissues like teeth and bones. As such an adhesive material to be used for wet bodies, a resin-based curable composition containing a radical polymerizable monomer, a polymerization initiator, etc., has been widely used.
Proposals that have been conventionally made to enhance the adhesive properties of the resin-based curable composition to a wet body, particularly to biological hard tissues, can be roughly classified into two types. Those are: a proposal about a radical polymerizable monomer having an acidic group intended to enhance the chemical/physical interaction with a substrate as a bonding target such as teeth and bones, and a proposal about a polymerization initiator intended to allow efficient polymerization and curing of the curable composition that contains a radical polymerizable monomer having an acidic group on biological hard tissues.
As a dental adhesive agent using such a resin-based curable composition, so-called self-etching-type adhesive agents have been widely used in recent years. In such a self-etching-type adhesive agent, a self-etching primer that contains a polymerizable monomer having an acidic group and a hydrophilic polymerizable monomer is first applied to the surface of tooth structure, and then a bonding material is applied thereon. Lately, a photocurable one-component dental adhesive agent having both functions as a self-etching primer and as a bonding material in combination has been put to practical use.
In order for such a dental adhesive agent to exhibit sufficient adhesiveness to tooth structure, particularly to dentin, it is necessary to have an decalcifying effect to allow an acidic component to dissolve the surface of dentin, a penetration effect to allow a polymerizable monomer component to penetrate into collagen of dentin, and a curing effect to allow the polymerizable monomer component that has penetrated therein to solidify to form a hybrid layer with the collagen.
When a resin-based curable composition is bonded to a wet body, it is often that, among the above-mentioned decalcifying effect, penetration effect, and curing effect, the curing effect is reduced because of curing inhibition due to oxygen present at the bonding interface, resulting in a failure to obtain sufficient bond strength. The curing inhibition of this type occurs remarkably, particularly when the curable composition is bonded to tooth dentin and bones that contain a large amount of oxygen.
Therefore, in order to suppress the curing inhibition due to oxygen contained in a wet body and to accelerate the polymerization curing reaction, a use of a redox polymerization initiator composed of a catalyst (oxidizing agent) and an accelerator (reducing agent) has been proposed.
Owing to significant development in curing light units, photocurable one-component dental adhesive agents have become widely used in dental clinics in recent years. However, such photocurable one-component dental adhesive agents cannot be used for restoration sites that are located out of the reach of light from a light irradiator, such as the lower bottom part of the inner part of a root canal, and the inner side of a restorative material.
On the other hand, in a dual cure-type curable composition using a redox polymerization initiator composed of an oxidizing agent and a reducing agent, the sites that are located out of the reach of light are cured by the redox polymerization initiator, and the sites that are located within the reach of light are cured in a short time by a photopolymerization initiator for which the polymerization curing time can be adjusted easily. The dual cure-type composition is used as a material for core construction when restoring a root canal part whose root canal has been formed by removing the tooth pulp of the root part in the case of very advanced dental caries.
The applicants have proposed a redox-curing type composition that contains a radical polymerizable monomer, and an oxidizing agent and a reducing agent of a redox polymerization initiator. In the redox-curing type composition, a water-soluble reducing agent is powder dispersed so that the curing reaction at the bonding interface is accelerated due to water in a wet body. For example, Patent Literature 1 proposes a redox curing-type nonaqueous curable composition that contains a liquid radical polymerizable monomer, an organic peroxide, and a powdery water-soluble reducing compound. The powdery water-soluble reducing compound is dispersed in the liquid radical polymerizable monomer to form the redox curing-type nonaqueous curable composition.
The redox curing-type nonaqueous curable composition according to Patent Literature 1 exhibits high adhesive properties also in the case of performing a pretreatment with a self-etching primer that has a high decalcifying effect and penetration effect before applying the composition to the surface of a tooth (Example 3, Patent Literature 1).